This invention relates to a drill assembly, and in particular to an eccentric earth boring drill assembly.
The drill assembly of the present invention was designed for drilling tough overburdens. The use of an eccentric assembly, i.e. an assembly having a bit eccentrically mounted at the bottom of a drill string results in the formation of a hole which is larger than the remainder of the drill string for facilitating insertion of a casing into a drilled hole. Drill tools with eccentric bits are disclosed, for example by U.S. Pat. Nos. 3,416,616, issued to H. H. Ahlgren on Dec. 17, 1968; 3,648,789, issued to A. S. Eriksson on Mar. 14, 1972; 3,753,470, issued to G. Lagerstrom et al on Aug. 21, 1973; 4,408,669, issued H. A. I. Wiredal on Oct. 11, 1983; 4,440,244, issued to H. A. I. Wiredal on Apr. 3, 1984 and 4,545,443 issued to H. A. I. Wiredal on Oct. 8, 1985.
A common problem with eccentric drill bits of the type described in the patent literature is that of removing the bit from the bottom end of the drill string following drilling. Another problem is that of replacing bits, which are commonly threaded into a mandrel or the like.
An object of the present invention is to provide solutions to the above defined problems in the form of a relatively simple drill assembly, which is easy and consequently relatively inexpensive to produce, and which facilitates penetration of a formation and aids casing insertion into a bore.
Another object of the invention is to provide a drill assembly including a bit of which can quickly and easily be connected to or removed from the remainder of the assembly.